The present invention relates to a pattern formation method including a step of reducing a size of an opening formed in a resist pattern by allowing the resist pattern to flow.
In fabrication process for a semiconductor integrated circuit device, a resist pattern formed by lithography has been further reduced in accordance with increase of the degree of integration of a semiconductor integrated circuit and refinement of a semiconductor device.
In particular, in the formation of a resist pattern having an opening used for forming a hole or a groove in a film to be processed, the contrast is lowered in the conventional lithography technique as the size of the hole or the groove is reduced. Therefore, it has become difficult to form an opening used for forming a fine hole or groove.
As countermeasure, technique has been proposed in which the size of a hole or groove opening formed in a resist pattern is reduced by allowing the resist pattern to thermally flow, whereby forming, in the resist pattern, an opening with a fine size beyond the limit of the lithography technique.
Now, the conventional pattern formation method will be described with reference to FIGS. 3A through 3E.
First, a chemically amplified resist material having the following composition is prepared:
Base polymer: poly((2-methyl-2-adamantyl methacrylate)-(γ-butyrolactone methacrylate) (wherein 2-methyl-2-adamantyl methacrylate: γ-butyrolactone methacrylate=50 mol %: 50 mol %) . . . 1 g
Acid generator: triphenylsulfonium nonafluorobutanesulfonate . . . 0.03 g
Solvent: propylene glycol monomethyl ether acetate . . . 4 g
Next, as shown in FIG. 3A the chemically amplified resist material having the aforementioned composition is applied on a substrate 1, so as to form a resist film 2 with a thickness of 0.5 μm. Then, as shown in FIG. 3B, the resist film 2 is irradiated for pattern exposure with ArF excimer laser 3 emitted from an ArF excimer laser scanner (with NA of 0.60) through a photomask 4 having a desired mask pattern.
Thereafter, as shown in FIG. 3C, the resist film 2 is subjected to post-exposure bake (PEB) at a temperature of 105° C. for 90 seconds. In this manner, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer because an acid is generated from the acid generator therein while an unexposed portion 2b of the resist film 2 remains insoluble in an alkaline developer because no acid is generated from the acid generator therein.
Next, the resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer (an alkaline developer) for 60 seconds, so as to form a resist pattern 7 having an opening 6 with a size W1 of 0.20 μm as shown in FIG. 3D.
Then, the resist pattern 7 is subjected to annealing 8 at 150° C., so as to allow the resist pattern 7 to flow as shown in FIG. 3E. In this manner, the size W1 (=0.20 μm) of the opening 6 is reduced to a size W2 (=0.15 μm).
Thus, a resist pattern having an opening with a fine size beyond the limit of the lithography technique can be formed.
However, as shown in FIG. 3E, the opening 6 whose size has been reduced through the flow is disadvantageously largely degraded in its cross-sectional shape.
Furthermore, variation in the size on a wafer plane of the openings 6, which have been reduced in the size through the flow, is 20% or more, which is disadvantageously too large.
If a resist pattern having such openings that have degraded cross-sectional shapes and are varied in their sizes is used for etching a film to be processed, the shape can be degraded or the sizes can be varied in resultant contact holes or interconnect grooves, which lowers the yield of semiconductor devices.